Earlier quoted context omitted.
Every person on Earth could agree that Earth is flat and it wouldn't affect the reality of whether or not extraterrestrials visit earth even a little bit.
The shared causal structure is the absence of facts and denial of science. Nearly every religion on earth also suffers from that in their gospel, where many fictitious and supernatural phenomena are bundled together and sold for truth.
And the facts are just ... released. It's the interpretation of the observations that are disputed. And unless you think they are all fake, the explanations that do not involve alien tech are non-trivial to say the least.
I'm not sure why you'd think there is any shared causal structure with flat earthers at all.